punctuated equilibrium

theory of, Biology. a hypothesis holding that the evolution of species proceeds in a characteristic pattern of relative stability for long periods of time interspersed with much shorter periods during which many species become extinct and new species emerge.

(pŭngk'ch-ā'tĭd) The theory that new species evolve suddenly over relatively short periods of time (a few hundred to a thousand years), followed by longer periods in which little genetic change occurs. Punctuated equilibrium is a revision of Darwin's theory that evolution takes place at a slow, constant rate over millions of years. Compare gradualism. See Note at evolution.